Part I: Orach Chayim

It is rabbinically forbidden to move things more than four cubits in
an unroofed private domain that is more than 100 cubits long or more
than 5000 square cubits in area that is not used for residential
purposes (see 358:1-14;359:1;360:1-3;362:1,4;372:2); and it is
permitted to move things between such a domain and a KARMELIS (see 346:3).

It is rabbinically forbidden to move things more than four cubits in a
courtyard or alley that is surrounded by partitions on only three sides;
to make it permissible, the custom is to construct an "entrance shape"
on the open side (see 363:26). On other ways of fixing the open side
see 363:1-35 and 365:7-8. These methods are effective even for a courtyard
or alley that is open at both ends (see 364:1); but converting a public
domain into a private domain requires doors that can be closed (364:2).
On alleys of complex shapes see 364:3-5; on alleys that have other gaps
in their walls see 365:1-3.

If a private domain such as a courtyard is shared by people who eat
separately (see 370:4-6) in permanent homes (see 366:2;370:8), things may
be moved freely within the shared domain, but it is rabbinically forbidden
to move things between the homes, or between them and the shared domain,
unless the people "combine" by contributing to a common collection of food,
called an ERUV CHATZEROS (see 366:1;372:1,6,8-19;375:2-4;376:1-4). On
the nature, quantity, collection, and storage of the ERUV see 366:3-12;
367:1;368:1-5;369:1;394:2-3. On which people may or must participate in
the ERUV see 353:1-2;355:5;363:31;365:3;370:1-8;371:1-6;389:1;391:2. Two
groups of people may make a common ERUV if their domains are connected;
see 372:3-19;373:1;374:1-4;375:1;378:1-5;379:1-2.

Similarly, when several courtyards are adjacent to the same alley, it is
rabbinically forbidden to move things between the courtyards and the
alley unless the residents in the courtyards form a "partnership" by
contributing to a common collection of food (386:1). On the nature and
storage of this food see 386:1,3-9; on what groups may or must form a
partnership see 386:2,9; on moving things within the alley if a
partnership was not formed see 388:1. When an alley forms a partnership,
the individual courtyards need not combine; see 387:1. On forming a
partnership for all or part of a [walled] city see 391:1 and 392:1-8.

If someone who must participate in an ERUV or partnership did not do so,
he may instead verbally annul his claim to a share in the common domain
(see 380:1-4;381:1-7;391:1;392:8); but if he is a non-Jew, the others
must rent his share from him for a token amount before they can make an
ERUV (see 382:1-20;383:1;384:1-2;385:2;389:1;390:1-2;391:1;392:8; on
irreligious Jews see 385:1,3-4).

When the food used for an ERUV or partnership is collected, the blessing
"...Who commanded us about an ERUV" is recited; see 366:13-15 and 395:1.
On collecting it on a holiday that precedes the Sabbath, or at twilight
on Friday evening, see 393:1-3; on cases of doubt see 394:1.